1. Field of Invention
This invention relates to fuses and is particularly related to an improved fusible element. More specifically, the present invention is concerned with a fuse element which, due to its novel construction, results in improved breaking capacity and thermal characteristics of the fuse.
2. The Prior Art
The simplest type of fusible element which is used in fuse construction is generally made of a metallic substance or alloy with a uniform cross section. When the current flowing through this type of fuse exceeds its rated capacity, heat is generated uniformly throughout the fusible element which causes temperature rise and, eventually, if the overload current is significantly higher than the rated capacity of the fuse, the fusible element melts at its middle section and the current flow will be interrupted. Generally, in this type of fuse, a current load as little as 135% of the rated capacity of the fuse results in substantial amount of heat generation and temperature rise which cause the fusible element to melt and interrupt the circuit. This fuse, therefore, has limited tolerance and is not suitable in many circuits.
In another type of fuse which is widely used in electrical and electronic circuits, the fusible element is also made of a metallic substance or alloy with a uniform cross sectional area, except for its mid-section which is usually 1/4 to 1/2 of the cross sectional area of the fusible element. When an overload current flows through this type of fuse, it will melt at its midsection in a short time without excessive heat generation. However, the flow of a large amount of an overload current through this type of fusible element often produces an electrical arc across its mid-section which grows in intensity in a very short time interval and causes melting of the adjacent portions of the fusible element. The heat generation is frequently so rapid and intense at the mid-section necessitating the use of arc-extinguishing materials to absorb the heat and gases generated by the electric arc. Otherwise, the fuse is apt to burst.
Accordingly, it is an object of this invention to provide a fuse which has improved arc-resistance and breaking capacity.
It is another object of this invention to provide such fuses with a fusible element which is of novel construction.
It is a further object of this invention to provide a fusible element which, when incorporated into a fuse, results in improved breaking capacity and thermal characteristics, and increased arc-resistance during the passage of overload current through the fuse.
The foregoing and other objects of this invention will be more clearly comprehended from the following detailed description of the invention taken in conjunction with the accompanying drawings which form part of this application.